The GA-MA790FXT-UD5P is an AM3 motherboard with DDR3, not AM2+. The only reason there's no support for Bulldozer on 790FX is money. There's a lot of low end 760-770-780 motherboards that support Bulldozer already. And the AGESA should be standard between BIOSes of the same manufacturer.

Its a little more risky with motherboards that don't have dual bios like Gigabyte. In case something goes wrong you'll have to reflash your BIOS using an eeprom programmer or hot flash your BIOS with another motherboard.